slight disclaimer i had this same bug except it was a spotlight not a light bulb so I can't promise this will work for you but you would think its the same bug just a different light, anyway what i did to fix this was delete all associated parts with the bugged light (any wire and generators connected to it) then i did a hard reset on my xbox. to do this just hold down the power button on the console for 5 seconds until it turns off. then i built the generator first then the light then connected them and the light returned. like i said for me a spotlight was bugged not a lightbulb but i hope this works for you too.
EDIT: SOMETHING I FORGOT
what i THINK causes this glitch is when you activate and deactivate the generator its connected to. hope this helps.
still experimenting, but im reading lots of people getting this online. I am experiencing it as well. Very frustrating.